In recent years, as a technology for improving fuel efficiency and the environmental protection performance of a vehicle, introduction of a bi-fuel engine system, which selectively switches between a liquid fuel, such as gasoline, and a gaseous fuel, such as compressed natural gas (CNG), and supplies the fuels to a single engine, has progressed. Generally, in this bi-fuel engine system, in the case of using the gaseous fuel, the highly pressurized gaseous fuel that is filled in a gas tank is decompressed to a desired pressure by a regulator, and is supplied to a fuel injection valve that is dedicated to the gaseous fuel.
An electromagnetic type shut-off valve is inserted in a fuel supply path ranging from the gas tank to the regulator, and initiation and stopping of the gaseous fuel supply may be switched between by controlling the open and shut states of the shut-off valve using a control device. For example, PTL 1 discloses a technology in which a pressure difference between positions before and after a shut-off valve is detected by using two pressure sensors, and a current value for opening the shut-off valve is controlled in correspondence with the detection result so as to appropriately control a supply timing of gaseous fuel to an engine.